Houston rapper Z-RO will not face felony criminal charges for allegedly beating his then-gf Just Brittany ... TMZ has learned.

According to court records, a grand jury failed to indict Z-RO Tuesday on felony assault charges. TMZ broke the story ... Z-RO's ex-gf claimed the rapper slapped, punched and dragged her around his house while holding a pistol.

Brittany even handed over an audio recording of the alleged beating, prompting cops to arrest Z-RO in July.